The main aim of this projects is to study the regulation of energy expenditure and energy intake in humans and identify metabolic risk factors of weight gain in children and adults. To assess resting energy expenditure we use indirect calorimetry (metabolic carts and respiratory chamber). To assess energy expenditure in free-living condition we use doubly labeled water. To assess energy intake and eating behaviors we use food frequency questionnaires, vending machines, and taste tests. To determine the neuroanatomical correlates of taste/hunger/satiation we use positron emission tomography. In the past year we have: a)completed the 5-y follow up of 200 10 y old Pima Indian children and identified several metabolic risk factors of obesity in childhood; b)studied 70 pairs of twins and obtained preliminary evidence on the heritability of energy expenditure due to physical activity; c)identified the first mutation of a brain receptor associated with lower energy expenditure in over 300 adult Pimas; d)identified and published the first map of the human brain responses to taste/hunger/satiation in 11 lean individuals; d)dicovered differential brain responses to satiation in 11 obese individuals.